Was hoping some Chinese member would say "Nuke Turkey" but it did not happened....
Anyway, 150,000 troop is a small number for a country like Syria. it's less than 10 division or 3 Corps.......Set aside whether or not Russia can afford to raise 150,000 reserve and send them to Syria, with 150,000 troop you are looking at defending 2 or 3 strategic town and that's it.
Beside, this is basically what ISIS wanted, more western or non-Muslim boots on the ground help ISIS sell the "infidel oppression" for recruitment. Basically it help ISIS portray they are the good guys in local villages.